The main circuit of the cooling device of an internal combustion engine according to the above-mentioned Patent Application is shown schematically in FIG. 1 of the accompanying drawings. As shown in this Figure, the cooling device comprises a main cooling circuit constituted by a supply line 1 of which the inlet is connected to the outlet of the internal cooling circuit of an internal combustion engine 2, by a radiator 3 of which the inlet connected to the outlet of the supply line 1 and by a return line 4 of which the inlet is connected to the outlet of the radiator 3 and of which the outlet is connected to the inlet of the internal cooling circuit of the engine 2. A pump 5 driven by a variable speed electric motor 6 is mounted on the return line 4. The radiator 3 is ventilated by a cooling motor fan unit comprising a fan 7 driven by a second variable speed electric motor 8. The variations in the speeds of rotation of the electric motors 6 and 8 are controlled by an electronic control system 9 which receives the measurements transmitted by two temperature sensors of a coolant, such as water. One of these temperature sensors 10 is installed at the outlet to the engine 2 while the other one 11 is installed at the inlet to the engine 2. A by-pass 12 is connected to the return line 4 upstream of the pump 5 and to the supply line 1 downstream of the sensor 10 and upstream of a thermostatic valve 13 arranged on the line 1.
This thermostatic valve 13 is a conventional thermal valve of which the driving element is an expandable wax-type thermostatic bulb and it operates according to the all or nothing principle which means that it remains closed when the coolant has not attained an adequate temperature. The coolant is thus recirculated in the motor unit until this temperature is attained. Once this temperature has been attained, the thermal valve 13 opens and heat exchange is effected in the region of the radiator 3. The electronic control system 9 thus effects hierarchical control of the driving speed for the pump 5, that is to say also of the flow-rate of fluid circulating in the engine 2 and the radiator 3, and of the speed of driving 7 of the cooling motor fan unit, that is to say also of the overall coefficient of exchange K of the radiator 3 which increases at the same time as the flow of liquid traversing the radiator 3 and the velocity of the air sweeping this radiator 3.
FIG. 2 is of the accompanying drawings shows a flow chart of the control provided by the electronic control system 9 for the device in FIG. 1. Herreinafter, the coolant temperature at the outlet of the engine 2 will be designated by .theta.MS, the temperature deviation between the engine outlet and inlet by .DELTA..theta.M, and this temperature deviation should not exceed a threshold of .DELTA..theta.ML of which the value is fixed by the mechanics; the limit temperature for the rapid heating up of the engine 2 by .theta.F; the temperature at which the thermal valve 13 opens by .theta.V; and the threshold for closure of the thermal valve 13 can be considered, for simplicity, as equal to .theta.V, taking into account its hysteresis, .theta.V-.DELTA..theta.V; the safety limit temperature which .theta.MS should not exceed by .theta.MSL; and a reference value on which .theta.MS is based after opening the valve 13 by .theta.MSR.
Starting from an initial configuration 14 in which the speeds of the pump 5 and of the fan 7 are zero and the engine 2 at rest, if the engine is started up, it firstly has a heating-up phase in which, as shown at 15, the temperature .theta.MS is below the threshold .theta.F fixed, for example, at 60.degree. C., the pump 5 is driven at 16 at a minimum speed V2 which may be very low, and even zero, to allow a very rapid rise in the temperature of the liquid as the valve 13, which is closed, shuts off flow to the radiator 3 and directs the coolant towards the pump 5 via the by-pass 12. During this phase, the deviation .DELTA..theta.M is not significant.
When .theta.MS is observed at 15 to have attained .theta.F, the pump 5 is driven at a minimum speed V1 which is not zero and is higher than V2 and sufficient to allow circulation of the coolant in the ancillary cooling circuit (not shown). The control system 9 controls the speed V1 such that .DELTA..theta.M, does not exceed .DELTA..theta.ML, a limit value fixed, for example, at 7.degree. C. This is ensured by maintaining the speed of the pump 5 at the value V1 while .DELTA..theta.M is lower than or equal to .DELTA..theta.ML, then by increasing this speed once .DELTA..theta.M exceeds .DELTA..theta.ML until .DELTA..theta.M becomes equal to .DELTA..theta.ML again.
It should be checked at 17 whether .theta.MS is higher than or equal to .theta.V, a temperature fixed, for example, at a value between 85.degree. and 95.degree. C. If this is not the case, the valve 13 remains closed at 18, the speed of the fan 7 still being zero at 19 and it is thus checked at 20 whether .DELTA..theta.M is higher than .DELTA..theta.ML.
If this is the case, the speed of rotation of the pump 5 is increased at 21 until it is observed at 20 that .DELTA..theta.M is again equal to .theta.ML. The speed of the pump 5 is then adjusted at 22 to its minimum value V1, which is not zero.
If it is observed at 17 that .theta.MS has become higher than the threshold .theta.V, the thermostatic valve 13 opens at 23.
A test and an action which constitute a safety operation have been shown at 24 and 25 respectively. If .theta.MS exceeds the value .theta.MSL fixed, for example, at 105.degree. C., or if one of the two sensors 10 or 11 is short circuited or cut, the test 24 triggers the action 25 which sets the pump 5 and the fan 7 at maximum speed without taking into consideration .DELTA..theta.M.
It is checked at 26 whether .DELTA..theta.M is higher than .DELTA..theta.ML. If this is the case with the speed of the fan 7 still zero, the speed of the pump 5 is increased at 27 until the moment when .DELTA..theta.M is less than or equal to .DELTA..theta.ML.
After opening the valve 13, the speed of the pump 5 is controlled by the control system 9 to the temperature .theta.MS so that the temperature .theta.MS is based on the reference value .theta.MSR fixed, for example, at 95.degree. C.
However, the deviation .DELTA..theta.M is compared with .DELTA..theta.ML at each moment. If it exceeds the limit value .DELTA..theta.ML, the speed of the pump 5 is controlled to the difference .DELTA..theta.M-.DELTA..theta.ML, and this speed increases to a value which is sufficient for this difference to be cancelled. This generally takes place to the detriment of the temperature .theta.MS, which diminishes. If the reduction of the temperature .theta.MS is such that this temperature again becomes less than or equal to the threshold .theta.V, the valve 13 intervenes so that the temperature .theta.MS is maintained at the level of the threshold .theta.V.
If it is determined at 28 that .theta.MS is equal to .theta.MSR, no correction is made. On the other hand, if this is not the case, it is checked at 29 whether .theta.MS is higher than .theta.MSR. If this is the case, it is checked at 30 whether the pump 5 is already driven at its maximum speed. If so, the fan 7 is then driven at 30 at a speed which increases until the moment when .theta.MS is brought back to .theta.MSR. If not, the speed of the pump 5 is firstly increased at 32 until equality is obtained .theta.MS=.theta.MSR. The fan 7 is driven by the action 31 only when said pump 5 has attained its maximum value without being able to reduce .theta.MS to .theta.MSR.
If it is observed at 29 that .theta.MS is lower than .theta.MSR, it is checked at 33 whether the fan 7 is at rest. If this is the case, the reduction of the speed of the pump 5 is controlled at 34 until the moment when .theta.MS is again equal to .theta.MSR. If this is not the case, the driving speed of the fan 7 is firstly reduced at 35 so that .theta.MS is brought to .theta.MSR then, if .theta.MSR has still not been reached after the stoppage of the fan 7 observed at 33, the speed of the pump is reduced at 35 to bring .theta.MS back to .theta.MSR.
It is observed that the thermostat 13 only intervenes during control by means of control system 9 when .DELTA..theta.M becomes higher than .DELTA..theta.ML, in which case it is necessary to increase the speed of the pump 5 until the difference .DELTA..theta.M-.DELTA..theta.ML is cancelled. This is demonstrated by the heat exchange equations in the region of the radiator 3: EQU Q=mR.multidot.C.multidot..DELTA..theta.R.perspectiveto.mR.multidot.C.multid ot..DELTA..theta.M =K(.theta.RE-.theta.a).apprxeq.K(.theta.MS-.theta.a),
wherein Q represents the quantity of heat carried off; mR, the mass flow rate of the liquid in the radiator; C the specific heat of the liquid; .DELTA..theta.R, the temperature deviation between the inlet and outlet of the radiator 3; .theta.RE, the temperature of the coolant at the inlet of the radiator 3; and .theta.a, the temperature of the ambient air; .DELTA..theta.M, K and .theta.MS having been defined above.
Now the fact that the speed of the pump 5 is raised to reduce .DELTA..theta.M increases the coefficient K, therefore the quantity of heat carried off Q which causes cooling of the liquid which may go as far as closing the thermostat 13 since .theta.MS, which diminishes, can become less than .theta.V-.DELTA..theta.V, as indicated above. In critical cases in which the thermostat 13 will play its conventional role as temperature regulator, all the electronic components provided become useless.